The present invention relates to a microprocessor based implantable cardiac device, and more specifically to a microprocessor system having dual clock control to reduce the current drain of the microprocessor.
In implantable devices, such as implantable pacemakers and defibrillators, it sometimes is appropriate to provide a plurality of timing signals at various frequencies. For example, a single clock frequency can be chosen to drive a set of continuously clocked timers and the microprocessor in the implantable device, and the microprocessor can be capable of assuming either a sleep mode or a run mode. The run mode could be triggered by one of a plurality of presettable timers timing out, the occurrence of an asynchronous event such as an R-wave sense, telemetry interrupt information, etc. However, a single clock system does not provide the optimal frequency for driving either the microprocessor or each of the individual timers.
Specifically, in such systems, the frequency provided to the timers generally would be too high, if taken directly from the clock source. Therefore, the source clock signal must be divided down to drive the various presettable timers, such as for example, timing the various intervals in a pacing algorithm. This frequency division of the source clock signal is a waste of power.
In addition, to partially reduce power requirements, the frequency provided to the microprocessor by the clock source typically would be lower than that at which the microprocessor is capable of running. Therefore, either the source clock signal would have to be multiplied to a higher frequency, of the slower frequency would be used to drive the microprocessor. Under the latter situation, the microprocessor would have a slower response time to external stimuli and thus have a limited overall processing capability, particularly in the implementation of a complex computation algorithm.